Mutations parallel queries, except that the root field resolvers may make changes to underlying data in addition to exposing data.

The field resolver for a mutation will, as with a query, be passed nil as its value argument (the third argument). A mutation is expected to perform some state changing operation, then return a value that indicates the new state; this value will be recursively resolved and selected, just as with a query.

Mutations are defined as fields of the Mutation object.

When a single query includes more than one mutation, the mutations must execute in the client-specified order. This is different from queries, which allow for each root query to run in parallel.

Typically, mutations are only allowed when the incoming request is explicitly an HTTP POST. However, that is beyond the scope of Lacinia (it doesn’t know about the HTTP request, just the query string extracted from the HTTP request).